Methods and compositions for controlling fires



States met METHODSAND COMPOfiITIONS FOR CONTROLLINGLES George A.Connelblaos Angeles, Califqassignor to United States. Borax 8avChemical- Corporation, Los' Angeles, Calif.,:a;corporation of N evada.-.

No Drawing. Application ll iareh 29, 1%? Serial'No. 649,291"

Thisinvention hasto do with methods andcomposi-v tions for controlling.fires;

Whereaswthe invention .;is useful for. many different.

types offirecontrol, it isespeciallyefiective as an aid in checkingor.preventing the/spread of fires.

An importantpurpose' of the present invention is toprovidemeansandmethods for. treating solid fuel in the path of a fire toreduce its flammability and thereby to cluding light brush, leaves. andgrass, as welLas heavybranches...and :tree. trunks; and, also .includesother solid combustible materials; such. asuare'. commonly involvedin.structurakfires...

In controlling. .fir'es .in;many types of. fuel, particularly inthepresenceof. strong. winds, .it is often.difiicult or impossible toattack the fire directly where it,-is.burning,

intensely. i. That isespecially. true of fires in .forests and inthickbrush and scrubsgrowths, such as abound. in.-

the-southwestern'part. ofytheUnited:States. :Under suchconditionsitishighly desirable tolimit thespreadrof the fire. Thatissometimes; attempted by clearing away the fuel; from an.area.in. thepath ofthe fired However, to

beefiective, such-clearing mustbefairly complete within astrip'ofappreciable width. Once at fire hasstartedrit isusually. difiicult. orimpossible. to. prepare such; a cleared strip: rapidly. enough to. beeffective.

Previously-available.methods for..treating fuel to reduce itsflammability have; been relatively ineffective: for thepresenttpurposefl' For example, spraying.- the fuelqwithwater,inadvance.,of-..a firelmayfbe beneficial for a shorttime, ,butrthewaterutends to-hevaporate rapidly, particularly;asithe.fire approaches;That is especially true under conditions 10f: high wind and/om lowhumidity=,;; which often accompany dangerousfires;

a large scale. lations frequently-requires aisuccessionofdistinct steps,

sometimes;-separatedbydefinite time: intervals, -for-example .tQ.permit- .-.drying.a And" many. such previously.

knowmtreatmenta compositions. are efiectiveonly if the treated.-.materiaL. is deeply penetrated by. the, chemical;

tion. are toaprovidma relatively economical.composition.r whichis,.effective toreducefiammabilityof a. .widevariety:

ofsolid 'f'ue'ls', including those typicallyrinvolved instructural'fires as well as all types of vegetation; WhiChiS:

Qfi'ective when applied primarily to surface areas of the Patented. Nov.4,1958

fuel; and which becomes effective immediately upon applicationandremains fullyefiective thereafter at least for a period of hours ordays.

In'accordance with one aspect of the invention, fuel in the path of afire iscoated with anadherent layer consisting esssentially of solidcalcium-containing borate.

The borate layer may also contain any suitable-type of binder and may,if desired, include-other fire-retardant ingredients. Relatively minorproportions of further additives, such as willbetypically described, mayalso;be'

included. I have discovered that such a layerof calciumcontaining boratecan be formed on surfaces ofsolid fuel of substantially any type'byapplying tothe-fuel a suspension ofsolid finely dividedborate particlesin an aqueous medium.

It is preferred to include in that suspension a suitable stabilizingagent to render the suspensionstable vduring storage and transportation.Preferred stabilizing agents.

are those which render thesuspension thixotropic; and

which also act'asa binder for the borate particles after applicationofthe suspension to'the fuel.

An important advantage of the present invention is thatthe concentrationof active fire-retarding agent in the treating composition is notlimited, as in many previously available fire-retardantcompositions, byconsiderations of solubility. Hence the low solubility in water of,calcium-containingborates does not prevent their. elfective applicationto the fuel by the methods of the invention. That'is accomplished byapplying, the boratein the form of an aqueous suspension, rather than asa solu-.

tion.

The compositions of the invention may be employed in a wide variety ofways. for application to fuel in the-path of a fire tocheck itsspreading. Since-suchapplication may be made rapidly andbecomesefiective immediately, the invention. is particularly valuable:for checking the spread of existing plied to fuel in the path of a fireeither closely in advanceof the fire or while the fuel is alreadyactively burning. That type of application, which may often'be madeadvantageously from aircraft, is particularly well adapted forcontrolling forest fires in which the upper branches of trees areburning. Such fires are commonly known as crownfires and areparticularly difficult to control with previously available methods.

In the present specification and claimsthe phrase in the path of a fireincludes potential-as well as existing fires, and includes not onlyportions of the fire path well in advance of any existing fire, but alsoportions that are already burning.

A particular advantage of the'calcium-containing borate coatings of theinvention for the present purpose is that they are very light in color,typically white or substantially white. That fact, provides adistinctive ap pearance of treated areas, showing clearly whichareashave been treated and which have not. It also facilitates observation ofthe degreeof coverage that has been attained, permitting maximum economyof material without sacrifice of effectiveness. That is especiallyimportant in combatting firesinremote locations, where economy ofmaterial isv often critical.

One illustrative calcium-containing borate that may be They areparticularly useful:-

employed in the invention is the sodium-calcium borate that correspondsessentially to the formula Sodium-calcium borate of that type isavailable, for example, as a naturally occurring mineral known asulexite. Ulexite is mined especially in Kern County, California, and isalso imported from Chile. Ulexite is known both in massive form and in afilimentary form known as cottonball.

Another illustrative calcium-containing borate is the calcium boratethat corresponds essentially to the formula Ca B O -H O. Calcium borateof that type is available as the naturally occurring mineral known ascolemanite, which is mined, for example, in Inyo County, California.

A further example of calcium-containing borate, which is particularlyconvenient and effective for the present purpose, is a type of naturalore that is essentially a mixture of colemanite and ulexite and containsalso an appreciable proportion of insoluble gangue material. Natural oreof that type is mined, for example, at Shoshone in Inyo County,California. For convenience of description, that type of ore will bereferred to herein as Shoshone ore,-but without implying any limitationas to actual origin. A typical variety of such Shoshone ore containssubstantially 58% ulexite, 23% colernanite and the remainder insolublegangue. The borate components of such ore may thus be characterized asso dium oxide, calcium oxide and boron trioxide in an overall relativeratio approximating 1:328, respectively, by weight. The insoluble gangueof Shoshone ore is useful in aiding formation of an aqueous suspensionof the ore and in stabilizing the resulting suspension, but, from thestandpoint of the direct fire retarding action of the resulting coatingon the fuel, the gangue is not an essential component of thecomposition.

'It is desirable that the calcium-containing borate be finer than about50 mesh. Superior results are obtained when it is ground to such arelatively fine mesh size, for example, that about 80% of the materialwill pass a No. 200 U. S. Standard screen. When coarser material is usedit is preferred to exclude any particles larger than about 50 mesh, bothto avoid risk of clogging the spray nozzle and because larger particlesreduce the strength and adherence of the resulting coating on the fuel.

In accordance with the invention, calcium-containing borates such asthose illustratively described can be applied to surfaces of fuel as anaqueous suspension and is then immediately appreciably more effectivethan a corresponding weight of water for checking a fire. Moreover, uponevaporation of the liquid water, such an aqueous suspension will form asolid, hard and remarkably durable coating. That coating layer has beenfound to greatly reduce flammability of the fuel. That result isparticularly striking when the fuel is exposed briefly to a very hotfire, as typically occurs, for example, in wild brush and forest fires.

Such reduction in flammability of fuel is obtainable with suspensions ofcalcium-containing borate over a wide range of borate concentrations. Ingeneral, effective results may be obtained with compositions comprisingfrom about 2 lbs. to as much as lbs. or more of ca1cium-containingborate per gallon of water. For any particular application, the mosteffective concentration of calciumcontaining borate in the aqueoussuspension depends upon such factors as the nature of the fuel to betreated, the detailed manner of application and the amount and type ofstabilizing agent, if any, that is included in the composition. Undermost practical conditions the preferred compositions contain from about3 to about 8 pounds of calcium-containing'borate per gallon of water. Itis often convenient, however, to make up a stock suspension containing arelatively large concentration of solid ingredients, for example, from 8to 20 pounds per gallon of water, and to dilute that stock solution withwater to increase its fluidity before actual use.

Any convenient mixing procedure may be employed in preparing the aqueoussuspension of borate. Measured quantities of Water and of dry granularingredients may be added to a mixing tank provided with any suitableautomatic agitating means. Such means may comprise, forexample, apaddle-type agitator or a centrifugal pump with a by-pass connectionfrom the pump outlet back to the bottom of the tank. The resultingmixture is stirred until a uniform suspension is obtained. It ispreferred to include a suitable agent to render the suspension stable,so that, once mixing is completed, agitation may be stopped, at leastuntil just before the suspension is to be used.

The aqueous suspension may be distributed over the fuel surface in anyconvenient manner. Application by spraying is particularly rapid,effective and economical when the fuel to be treated is reasonablyaccessible. It is preferred to utilize a type of nozzle that produces afine spray, one such nozzle being known as a Bean spray gun. A pumppressure of about 100 to 200 pounds per square inch is preferred, buteffective coverage can usually be obtained with much lower pressuressuch as are typically available with fully portable equipment. Whensuitable power pumps are available, a nozzle opening of about inch hasbeen found effective and will typically deliver from 4 to 8 gallons ofsuspension per minute.

The compositions of the invention are also particularly well suited foraerial distribution. For example, an aircraft of the type employed forspraying crops may be fitted with tanks having a valve-controlled outletof large I diameter, typically 6 to 24 inches, for rapid dumping of afound in the lower hills of Southern California may be' effectivelytreated in most instances by applying to the vegetation on each squarefeet of ground surface 5 from about 10 to about 20 pounds ofcalcium-containing borate in the form of an aqueous suspension per 100square 7 By such application strips of treated fuel of suitable widthmay be prepared, extending feet of ground surface.

across the path of the fire. The most advantageous width for such stripsvaries with such factors as the detailed nature of the fuel, the slopeof the ground and the amount and direction of the wind. It has beenfound, in general, that a fire can be effectively checked by so treatinga strip of about the same width that would be required if the groundwere completely cleared of vegetation. Thus a strip 4 to 6 feet Wide isusually suflicient to check a fire on level ground in absence of wind,whereas a strip 6 to 8 feet wide or more may be preferable under lessfavorable conditions. Backfiring has been successfully carried out froma strip 2 to 4 feet wide treated as described by crews moving throughgrass and light brush at a fast walk.

When trees or clumps of tall brush occur inside a fire line of thedescribed type, it is desirable to treat the surface fuels at the baseof the trees and also the lower part of each crown. For example, scruboak treated in that manner typically does not ignite and crown out,whereas untreated trees of the same type burn readily, producing aserious source of spot fires.

Suspensions of calcium-containing borate can be rendered stable for anindefinite period by providing asuitable stabilizing agent. A preferredtype of stabilizing agent comprises a finely divided inorganic solidwhich is chemically inert with respect to the borate and which rendersthe solutionthixotropie'; Clays-.of'ithe montmorile for the presentpurpose. Illustrative.of;such* days are hectorite and Wyoming bentonite.Such clays may be combined with calcium-containing borate,suchaszul'exite, colemanite, or a mixture. of thensame, innaratiotofclayto borate. of from about 1:20 to 'about.1:4to' give-the boratesuspension. a -useful degree oftstability. Effective stabilitymay alsobe. produced,- for example, with a-ttype of clay that is commonlyavailable-under .thetradename Aquagel. A further example of a usefulstabilizing agent is .the insoluble gangue portion-ofthe natural orealready referredI-to as C ore;. Thatgangue comprises primarily a shalethat tends to break down on'wetting into a fine clay. Becauseofthatiaction.of:the insoluble component, finely divided-C oremaybesuspended directly in water without other additive to produce asuspension that is remarkably stable and effective overawide range ofconcentrations.

Stabilizing agents of the type just described have the particularadvantage that,:upon drying of the composition after applicationtothefuel, they act-as-a-bindert-which tends to improve the uniformityanddurability of the coating-that is produced. By thus improvingthe'physicalnatureof the coating layer, stabilizingagents of the-described type contribute *appreciablyto therpractical eifeca tiveness ofthe treatingcompositionsr That indirect ac.- tion, however, is to beclearly distinguished. from the direct fire retarding action of thesolidcalcium-containing borate, which preferably comprises the major portionof the coating layer.

Further additives may advantageously-beincluded in the compositions ofthe invention. .For example, it is sometimes desirable to provide aminor proportion of a wetting. agent to promote uniform-wettingofthe'fuelsurface by the aqueous borate suspension. .Such enhancementofthe wettingqualities of the composition tends toproduce a.

more uniform and continuous coatingof the fuel, It may 7 also beextremely helpful in obtaining effective penetration of the suspensionto portionsv of the fuel thatare. partially hidden or enclosed, forexample penetration. mm thick brush or. into a thick coveringoflitteronthe ground. Useful wetting .agents. for such purposes include,.. for.example, aryl alkyl sulfonates, which. are available. under such tradenames as Oronite D-40 and Petro P."

Adherence to the fuel of the film, of solid calcium-containing boratemay be further increased by including in the composition a suitableminor proportion of a sticking agent, such asthe animal proteinmaterialfsold as a commercial sticking agent under the trade nameArmours Sticker; the long-chain fatty acidpreparation with di ethyleneglycol abietate which is available under the trade name DuPont Spreaderand Sticker; or the lignin sulfonate which is available under the tradename Orazan. From about 1 to about 10% of such sticking agents may bedesirable. The duPont preparation also acts as wetting agent and has theparticular advantage of not interfering with normal stability of thesuspensions.

The compositions of the present invention are well adapted forapplication to the fuel in the form of a foam. A suitable foam,consisting of a mass of very small bubbles of the fluid composition, maybe produced by adding to the herein described compositions an effectiveamount of a suitable foaming agent, and applying the composition to thefuel by spraying from a known type of foam-producing nozzle. From about1 to about 3% of a conventional foaming agent has been found to beeffective under most conditions.

Application of the compositions of the invention as a foam tends topromote their adherence to certain types of fuel which have an unusuallysmooth or waxy surface, such, for example, as the leaf surfaces ofManzanita brush. Moreover,'the foam can be built up on the fuel to aconsiderable thickness without consumption of an undue amount ofmaterial. It has been found particular- 1y effective-under some.conditionslorinclude a 'foamirfgz' agent in: compositions forapplicationzby aerial dropi Up-;-. on release from the aircraft the;suspension then becomes;

a light, fluify and expanded material capable ofrcovering a relatively:large area.

The :following: particular: compositions are :described'i as illustrati'onsof the wide :varietyofcompositionsawithinthez: scope of.theminventiont. However; that scope is not in= tended tobelimited-bytparticulars of theillustrative ex amples, but is defined bythe appended claims;

Example 1=.An. illustrative "and;- highly effective-compositiominaccordance with th-cipresent iI1V6I1tl0I1'.WaS" prepared by grindingulexite to a particle size such-that:

substantially 80% passed a 200. mesh" screen-rand. suspending thewfinelydivided=ulexite in'water ata concen-.: tration of 4-pounds-ofrulexiterper gallon. of water. :The resulting suspension waseffectively. stable for;periods1.of:

the order of onehour, and could be maintained fluid for longer-timeperiods .-by mild agitation". tions containing from about 3 to about '8pounds. of ulexite per gallonrofwwaterare: also highly t-satisfactory.

Example 2.Finely divided. ulexiteaof'the typ-eem:

slightly; viscous suspension 1 which was 1 highlyrstable and could.bewstored for several days without; significant settling.

' Example: 3: Colemanite: was ground. to predominantly pass a 200 meshscreen and was suspended. in water in a concentration. of'4 pounds pergallon..of.;water.; .The. resulting-suspension was similar to that. ofExamplel Colemanite may also be; employed at concentrations.

from about 3 to 8 pounds per gallon.of.water. .'I'he stability of; suchsuspension can be. greatlyincreasedby addition of astabilizingv agent ofthedescribed' type, for example hectorite, in a ratio'of' about 0.05to.0.2.pound of agent-.per pound of colemanite;

Example. 4 ;-A particularly economical andiconvenient compositionconsists essentially of an aqueous'suspem sion of finely groundshoshonesore'; already described;

For example, such ore was ground to. a particlesize predominantly minus200 mesh and'stirred in water atconcentrations of about 3 to about 8-pounds per gallon of water, the preferred .value. being approximately 4'pounds per'gallon of water.: The resultingisu'spensions' were highlystable and could readily'zbe handled by hydrauliotmethods;

Example 5.Ulexite and colemanite were finely ground and suspended inwater in a ratio of approximately 5 pounds of ulexite and 2 pounds ofcolemanite per gallon of water. Stability of the resulting suspension isadequate for many purposes, but may be greatly increased by adding astabilizing agent of the type described, for example a Wyomingbentonite, in a ratio of from about 0.05 to about 0.2 pound of the agentper pound of the other solid ingredients.

All of the compositions illustratively described in Examples 1 through 5give satisfactory surface coverage on many types of fuel. Under certainconditions that action may be further improved by the use of furtheradditives, as has already been described.

An indication of the effectiveness of the compositions of the inventionwas obtained by assembling a pile of cut dry brush approximately 12 feetin diameter and 6 feet high. The downwind half of the pile was thensprayed with the composition of Example 4 in sufiicient quantity to coatsubstantially all exposed surfaces of the fuel. Evaporation of the waterleft the fuel coated with a hard dry solid film consisting essentiallyof calciumcontaining borate. The untreated half of the brush pile wasthen set on fire. The untreated brush burned hotly and was substantiallyconsumed in a few minutes. Most Composi-I' of the treated brush remainedunburnt. tions illustratively described in the other examples aresimilarly effective in checking the spread of fires.

I claim:

1. A composition for coating surfaces of fuel in the path of a fire toretard the same, said composition consisting essentially of an aqueoussuspension of finely divided solid calcium-containing borate in aconcentration between about 3 and about 20 pounds of said borate pergallon of water.

2. A composition as defined in claim 1, and in which the solidcalcium-containing borate consists essentially of ulexite.

3. A composition as defined in claim 1, and in which the solidcalcium-containing borate consists essentially of calcium borate andsodium-calcium borate in a weight ratio of approximately 2 to 5.

4. A composition as defined in claim 1 and in which the solidcalcium-containing borate is predominantly finer than about 50 mesh. 7

5. A composition for coating surfaces of fuel in the path of a fire toretard the same, said composition consisting essentially of an aqueoussuspension containing from about 3 to about 20 pounds per gallon ofwater of solid finely divided solid calcium-containing borate andcontaining also a finely divided substantially insoluble solidstabilizing agent in a concentration between about & and about A that ofsaid borate, said stabilizing agent rendering the suspension stable andthixotropic.

6. A composition for coating surfaces of fuel in the path of a fire toretard the same, said composition consisting essentially of an aqueoussuspension of a finely divided natural ore in a concentration betweenabout 3 and about 20 pounds per gallon of water, said ore consistingessentially of sodium borate, sodium-calcium borate and insolublegangue.

7. A composition for coating surfaces of fuel in the path of a fire toretard the same, said composition consisting essentially of an aqueoussuspension containing between about 3 and about 20 pounds per gallon ofwater of a finely divided solid borate composition comprising sodiumoxide, calcium oxide and boron trioxide in overall relative proportionsapproximating 1:3:8, respectively, by weight.

8. The method of retardin'g fire in solid fuel that has an exposedsurface; said method comprising forming on a major portion of the fuelsurface a substantially continuous adherent layer consisting essentiallyof solid calcium-containing borate.

9. The method of retarding fire in solid fuel that has The composi- Ythe class consistingof calcium borate and sodium calcium borate.

10. The method of retarding fire in solid fuel that has an exposedsurface; said method comprising forming on a major portion of the fuelsurface a substantially continuous adherent layer of a natural oreconsisting essentially of calcium borate, sodium-calcium borate andinsoluble gangue.

11. The method of retarding fire in solid fuel that has an exposedsurface; said method comprising distributing over the fuel surface anaqueous suspension of solid granular calcium-containing borate, theparticle size of said borate being predominantly finer than about mesh,and the rate of application of the suspension being suflicient toproduce, upon evaporation of water there from, a solid coating over amajor portion of the fuel surface.

12. The method of retarding fire in solid fuel that has an exposedsurface; said method comprising distributing over the fuel surface anaqueous suspension of granular natural ore consisting essentially ofcalcium borate, calcium-sodium borate and insoluble gangue, the particlesize of the ore being predominantly finer than about 50 mesh, and therate of application of the suspension being sufficient to produce, uponevaporation of water therefrom, a solid coating over a major portion ofthe fuel surface.

13. The method of retarding fire in solid fuel that has an exposedsurface; said method comprising distributing over the fuel surface anaqueous suspension containing between about 3 and about 10 pounds pergallon of Water of a finely divided solid borate composition comprisingsodium oxide, calcium oxide and boron trioxide in overall relativeproportions approximating 1:3:8, respectively, by weight, the rate ofapplication of the suspension being suificient to produce, uponevaporation of water therefrom, a solid coating over a major portion ofthe fuel surface.

14. The method defined in claim 11 and in which the said aqueoussuspension is distributed over the fuel surface in the form of a foam.

References Cited in the file of this patent UNITED STATES PATENTS

1. A COMPOSITION FOR COATING SURFACES OF FUEL IN THE PATH OF A FIRE TORETARD THE SAME, SAID COMPOSITION CONSISTING ESSENTIALLY OF AN AQUEOUSSUSPENSION OF FINELY DIVIDED SOLID CALCIUM-CONTAINING BORATE IN ACONCENTRATION BETWEEN ABOUT 3 AND ABOUT 20 POUNDS OF SAID BORATE PERGALLON OF WATER.